mshtml: Implement HTMLPerformance's toString.

dlls/mshtml/omnavigator.c

@@ -2161,8 +2161,10 @@ static HRESULT WINAPI HTMLPerformance_get_timing(IHTMLPerformance *iface, IHTMLP
 static HRESULT WINAPI HTMLPerformance_toString(IHTMLPerformance *iface, BSTR *string)
 {
     HTMLPerformance *This = impl_from_IHTMLPerformance(iface);
-    FIXME("(%p)->(%p)\n", This, string);
-    return E_NOTIMPL;
+
+    TRACE("(%p)->(%p)\n", This, string);
+
+    return dispex_to_string(&This->dispex, string);
 }
 
 static HRESULT WINAPI HTMLPerformance_toJSON(IHTMLPerformance *iface, VARIANT *var)

dlls/mshtml/tests/documentmode.js

@@ -216,6 +216,7 @@ sync_test("builtin_toString", function() {
     if(localStorage) test("localStorage", localStorage, "Storage");
     test("location", window.location, "Object", window.location.href);
     test("navigator", window.navigator, "Navigator");
+    test("performance", window.performance, "Performance");
     test("screen", window.screen, "Screen");
     test("sessionStorage", window.sessionStorage, "Storage");
     test("style", document.body.style, "MSStyleCSSProperties");